Dietz best attachments are found in square and round tube versions ( this is a round tube ) and are an aftermarket accessory. 
They convert your standard barn tubular into a dash model , will fit a variety of models, best paired with late  1880s tubulars before dash models like the Buckeye were readily available. 

Patent date is June 15th 1886

Condition is excellent,  barn fresh natural patina.